Patent application title: ELECTRODE FOR A POWER STORING APPARATUS AND POWER STORING APPARATUS PROVIDED WITH THAT ELECTRODE

Abstract:

An electrode for a power storing apparatus has a collector and a plurality
of electrode patterns formed on at least one surface of the collector. An
electrode pattern in a region where heat is radiated less than in other
region, from among the plurality of electrode patterns, has a lower
formation density than an electrode pattern in the other region.

Claims:

1. An electrode for a power storing apparatus comprising:a collector; anda
plurality of electrode patterns with active material that are formed on
at least one surface of the collector,wherein an electrode pattern with
active material in a region where heat is radiated less than in other
region, from among the plurality of electrode patterns with active
material, has a lower formation density than an electrode pattern with
active material in the other region.

2. The electrode for a power storing apparatus according to claim 1,
whereinthe region where heat is radiated less than in other region is a
central portion on the collector, andthe other region is an end portion
on the collector.

3. The electrode for a power storing apparatus according to claim 2,
whereinan interval between adjacent electrode patterns with active
material on the central portion of the collector is formed larger than an
interval between adjacent electrode patterns with active material on the
end portion of the collector.

4. The electrode for a power storing apparatus according to claim 3,
whereinthe plurality of electrode patterns with active material are
formed such that the interval between adjacent electrode patterns with
active material becomes larger from the end portion on the collector
toward the central portion on the collector.

5. The electrode for a power storing apparatus according to claim 3,
whereineach of the plurality of electrode patterns with active material
has substantially the same size.

6. The electrode for a power storing apparatus according to claim 2,
whereina size of the electrode pattern with active material positioned on
the central portion of the collector is formed smaller than a size of the
electrode pattern with active material positioned on the end portion of
the collector.

7. The electrode for a power storing apparatus according to claim 6,
whereinthe plurality of electrode patterns with active material are
formed such that the size of the electrode patterns with active material
becomes smaller from the end portion on the collector toward the central
portion on the collector.

8. The electrode for a power storing apparatus according to claim 2,
whereina thickness of the electrode pattern with active material
positioned on the central portion of the collector is formed thinner than
a thickness of the electrode pattern with active material positioned on
the end portion of the collector.

9. The electrode for a power storing apparatus according to claim 1,
whereinwhen the electrode is cylindrically rolled up, an interval between
adjacent electrode patterns with active material on an inside in a radial
direction of the power storing apparatus, from among the plurality of
electrode patterns with active material, is formed larger than an
interval between adjacent electrode patterns with active material on an
outside in the radial direction of the power storing apparatus.

10. The electrode for a power storing apparatus according to claim 1,
whereinwhen the electrode is cylindrically rolled up, a size of an
electrode pattern with active material on an inside in a radial direction
of the power storing apparatus, from among the plurality of electrode
patterns with active material, is formed smaller than a size of an
electrode pattern with active material on an outside in the radial
direction of the power storing apparatus.

11. The electrode for a power storing apparatus according to claim 1,
whereinwhen the plurality of electrode patterns with active material are
formed substantially concentric on the collector, an interval between
adjacent electrode patterns with active material on a radial inside, from
among the plurality of electrode patterns with active material, is formed
wider than an interval between adjacent electrode patterns with active
material on a radial outside.

12. The electrode for a power storing apparatus according to claim 2,
whereina density of active material of the electrode pattern with active
material positioned on the central portion of the collector is lower than
a density of active material of the electrode pattern with active
material positioned on the end portion of the collector.

13. The electrode for a power storing apparatus according to claim 1,
whereinwhen a heat source is arranged adjacent to the power storing
apparatus, an electrode pattern with active material in a region adjacent
to the heat source, from among the plurality of electrode patterns with
active material, has a lower formation density than an electrode pattern
with active material in another region.

14. A power storing apparatus comprising:the electrode according to claim
1 which is used as at least one of a positive electrode and a negative
electrode.

15. A power storing apparatus comprising:a plurality of stacked
electrodes, each of the plurality of stacked electrodes including a
collector and a plurality of electrode patterns with active material
formed on at least one surface of the collector,wherein an electrode
pattern with active material in a region where heat is radiated less than
in other region among the plurality of stacked electrodes, has a lower
formation density than an electrode pattern with active material in the
other region, andthe formation densities of the plurality of electrode
patterns with active material among the plurality of stacked electrodes,
differ from one another depending on position of the electrode in the
stacking direction.

Description:

[0001]This is a 371 national phase application of PCT/IB2007/002392 filed
21 Aug. 2007, claiming priority to Japanese Patent Application No.
2006-228984 filed 25 Aug. 2006, the contents of which are incorporated
herein by reference.

BACKGROUND OF THE INVENTION

[0002]1. Field of the Invention

[0003]The invention relates to an electrode for a power storing apparatus,
which used in a power storing apparatus such as a secondary battery or a
capacitor, and a power storing apparatus provided with this electrode.

[0004]2. Description of the Related Art

[0005]An electrode (i.e., a positive electrode or a negative electrode)
used in a secondary batter or the like is known in which a uniform
electrode layer (i.e., a negative electrode layer or a positive electrode
layer) is applied to the entire surface of a collector. However, when the
electrode layer is formed on the entire surface of the collector, stress
that acts on the electrode, such as stress that is generated when the
electrode layer is formed or stress due to vibrations or the like from
the outside may cause cracks or the like in the electrode layer.

[0006]Japanese Patent Application Publication No. 2005-11660 (hereinafter
referred to as "JP-A-2005-11660") proposes a structure that alleviates
stress on the electrode by forming a plurality of minute cells as the
electrode layer on the collector. More specifically, a plurality of
minute cells are arranged in a matrix at equal intervals on the surface
of the collector. On the other hand, Japanese Patent Application
Publication No. 2005-71784 (hereinafter referred to as "JP-A-2005-71784")
proposes a structure that uses a plurality of cooling tabs and maximizes
the radiation effect of the cooling tabs provided near a center layer in
order to suppress variations in temperature between the the center layer
side and the outer layer side of a stacked battery.

[0007]However, in the electrode for a secondary battery described in
JP-A-2005-11660, the intervals between the plurality of minute cells
formed on the collector are set evenly, which has the following adverse
effects. With a battery having a stacked structure, for example,
generated heat during charge and discharge tends to build up in the
central portion more so than in the outer peripheral portion of the
electrode. When heat builds up in the central portion of the electrode,
the internal resistance of the central portion decreases, and as a
result, current tends to flow more easily through the central portion.
Large amounts of current flowing through the central portion promote heat
generation in the central portion so the internal resistance of the
central portion decreases even more. As a result, the electrode degrades.
Also, for the reason stated above, the temperature distribution on the
surface of the electrode is such that the temperature is highest at the
central portion and gradually drops toward the outer peripheral side.

[0008]Here, JP-A-2005-11660 mentions that the minute cells may be
regularly arranged in one region on the collector and irregularly
arranged in other regions. However, this structure alone is not enough to
uniformly distribute the temperature on the electrode. That is, with the
electrode for a secondary battery described in JP-A-2005-11660, the
minute cells are not arranged taking the temperature distribution on the
electrode into account.

[0009]On the other hand, with the stacked battery described in
JP-A-2005-71784, for example, the cooling tabs must be provided
separately so the number of parts is increased. Also, the structure
described in JP-A-2005-71784 changes the radiation effect in the
direction of thickness (i.e., in the stacking direction) of the stacked
battery, but does not take into account heat radiation based on the
temperature distribution in a direction orthogonal to the direction of
thickness of the stacked battery (in other words, the in-plane of the
collector).

SUMMARY OF THE INVENTION

[0010]This invention thus provides an electrode for a power storing
apparatus, which may suppress variation in the temperature distribution
on the electrode with a simple configuration, and a power storing
apparatus provided with that electrode.

[0011]An electrode for a power storing apparatus according to a first
aspect of the invention has a collector and a plurality of electrode
patterns with active material formed on at least one surface of the
collector. In particular, an electrode pattern with active material in a
region where heat is radiated less than in other region, from among the
plurality of electrode patterns with active material, has a lower
formation density than an electrode pattern with active material in the
other region.

[0012]Here, the region where heat is radiated less than in other region
may be a central portion of the collector, and the other region may be an
end portion of the collector.

[0013]Also, an interval between adjacent electrode patterns with active
material on the central portion of the collector may be formed larger
than an interval between adjacent electrode patterns with active material
on the end portion of the collector.

[0014]Further, the plurality of electrode patterns with active material
may be formed such that the interval between adjacent electrode patterns
with active material becomes larger from the end portion of the collector
toward the central portion of the collector.

[0015]In this case, each of the plurality of electrode patterns with
active material may have substantially the same size.

[0016]Moreover, a size of the electrode pattern with active material
positioned on the central portion of the collector may be formed smaller
than a size of the electrode pattern with active material positioned on
the end portion of the collector.

[0017]Also, the plurality of electrode patterns with active material may
be formed such that the sizes of the electrode patterns with active
material become smaller from the end portion of the collector toward the
central portion of the collector.

[0018]Further, a thickness of the electrode pattern with active material
positioned on the central portion of the collector may be thinner than a
thickness of the electrode pattern with active material positioned on the
end portion of the collector.

[0019]Moreover, when the electrode is cylindrically rolled up, an interval
between adjacent electrode patterns with active material on an inside in
a radial direction of the power storing apparatus, from among the
plurality of electrode patterns with active material, may be formed
larger than an interval between adjacent electrode patterns with active
material on an outside in the radial direction of the power storing
apparatus.

[0020]Also, when the electrode is rolled up cylindrically, a size of an
electrode pattern with active material on an inside in a radial direction
of the power storing apparatus, from among the plurality of electrode
patterns with active material, may be formed smaller than a size of an
electrode pattern with active material on an outside in the radial
direction of the power storing apparatus.

[0021]Also, when the plurality of electrode patterns with active material
are formed substantially concentric on the collector, an interval between
adjacent electrode patterns with active material on a radial inside may
be formed wider than an interval between adjacent electrode patterns with
active material on a radial outside.

[0022]Also, a density of active material of the electrode pattern with
active material positioned on the central portion of the collector may be
lower than a density of active material of the electrode pattern with
active material positioned on the end portion of the collector.

[0023]Also, when a heat source is arranged adjacent to the power storing
apparatus, the formation density of an electrode pattern with active
material in a region adjacent to the heat source, from among the
plurality of electrode patterns with active material, may be lower than
the formation density of an electrode pattern with active material in
another region.

[0024]Also, A power storing apparatus according to a second aspect of the
invention includes the foregoing electrode that is used as at least one
of a positive electrode and a negative electrode.

[0025]Also, A power storing apparatus according to a third aspect of the
invention includes a plurality of stacked electrodes. In particular, each
of the plurality of electrodes has a collector and a plurality of
electrode patterns with active material formed on at least one surface of
the collector. An electrode pattern with active material in a region
where heat is radiated less than in other region among the plurality of
stacked electrodes has a lower formation density than an electrode
pattern with active material in the other region. The formation densities
of the plurality of electrode patterns with active material among the
plurality of stacked electrodes, differ from one another depending on
position of the electrode in the stacking direction.

BRIEF DESCRIPTION OF THE DRAWINGS

[0026]The foregoing and further objects, features and advantages of the
invention will become apparent from the following description of example
embodiments with reference to the accompanying drawings, wherein like
numerals are used to represent like elements and wherein:

[0027]FIG. 1 is a front view of a bipolar electrode according to a first
example embodiment of the invention;

[0028]FIG. 2 is a side view of the bipolar electrode according to the
first example embodiment;

[0029]FIG. 3 is a graph showing the relationship between temperature and
position on the bipolar electrode;

[0030]FIG. 4 is a front view of a bipolar electrode used in a cylindrical
battery;

[0031]FIG. 5 is a view of a retaining structure of a bipolar battery;

[0032]FIG. 6 is a front view of a bipolar electrode according to a
modified example of the first example embodiment;

[0033]FIG. 7 is a side view of the bipolar electrode according to a
modified example of the first example embodiment;

[0034]FIG. 8 is a front view of a concentric bipolar electrode; and

[0035]FIG. 9 is a schematic showing the structure of an electrode pattern
in a bipolar electrode according to a second example embodiment of the
invention.

DETAILED DESCRIPTION OF EMBODIMENTS

[0036]In the following description and the accompanying drawings, the
present invention will be described in more detail in terms of example
embodiments.

[0037]A bipolar battery according to a first example embodiment will be
described with reference to FIGS. 1 and 2. Here, this bipolar battery may
be regarded as the "power storing apparatus" of the invention. FIG. 1 is
a front view of a bipolar electrode used in the bipolar battery according
to the first example embodiment, and FIG. 2 is a side view of the bipolar
type battery having a structure in which the bipolar electrodes are
stacked. Here, the bipolar electrode is such that a positive electrode
layer is formed on one side of a collector and a negative electrode layer
is formed on the other side of the collector. FIG. 1 shows one side of
the bipolar electrode (i.e., the side on which the positive electrode
layer is formed). In the first example embodiment, although FIG. 1 shows
the structure of the positive electrode layer on one side of the bipolar
electrode, the structure of the negative electrode layer on the other
side (i.e., the back side) is the same.

[0038]Also, in the following example embodiment, a bipolar type secondary
battery will be described, but the invention may also be applied to a
secondary battery that is not a bipolar type secondary battery. Here, in
a secondary battery that is not a bipolar type secondary battery, an
electrode in which an identical electrode layer (a positive electrode
layer or a negative electrode layer) is formed on both sides of the
collector may be used, or an electrode in which an electrode layer is
formed on only one side of the collector may be used. Further, in the
following example embodiment, a secondary battery is described, but the
invention may also be applied to a stacked capacitor (i.e., an electrical
double layer capacitor) that serves as the power storing apparatus. This
stacked capacitor is such that a plurality of positive and negative
electrodes are alternately stacked together with separators in between.
In this stacked capacitor, aluminum foil may be used for the collectors,
activated carbon may be used for the active material of the positive and
negative electrodes, and a porous membrane made of polyethylene may be
used for the separators.

[0039]Also, in the following example embodiment, a stacked battery is
described, but the structure of the battery is not limited to this. The
invention may also be applied to a battery other than a stacked (i.e.,
flat) battery, such as a rolled (i.e., cylindrical) battery.

[0040]In FIGS. 1 and 2, a bipolar electrode 1 has a collector 11 which
serves as a base. A plurality of electrode patterns 12a which serve as
positive electrode layers are formed (in the X-Y plane) on one side of
the collector 11. Also, a plurality of electrode patterns 12b which serve
as negative electrode layers are formed on the other side of the
collector 11 (see FIG. 2). The collector 11 may be made of, for example,
aluminum foil or a plurality of metals. Also, a metal surface covered
with aluminum may also be used as the collector 11. Incidentally,
although not a bipolar electrode, a so-called composite collector in
which plural sheets of metal foil have been laminated together may also
be used. When this composite collector is used, aluminum or the like may
be used for the material of the positive electrode collector and nickel
or copper or the like may be used as the material for the negative
electrode collector. A structure in which the positive electrode
collector and the negative electrode collector are in direct contact with
one another, or a structure in which a conductive layer is provided
between the positive electrode collector and the negative electrode
collector may also be used as the composite collector.

[0041]The electrode patterns 12a and 12b are formed with active material,
electrical conducting material, an additive, or the like, according to
the positive or negative electrode. Materials such as the following may
be used to make the electrode patterns 12a and 12b. For example, with a
nickel-metal-hydride battery, nickel oxide may be used for the active
material of the positive electrode of the electrode pattern 12a, and a
hydrogen-absorbing alloy such as MMNi.sub.(5-y-z)AlxMnyCo.sub.z
(Mm: Misch metal, an alloy of rare earth elements) may be used for the
active material of the negative electrode of the electrode pattern 12b.
Also, in a lithium secondary battery, lithium-transition metal composite
oxide may be used for the active material of the positive electrode of
the electrode pattern 12a, and carbon may be used as the active material
of the negative electrode of the electrode pattern 12b. Also, acetylene
black, carbon black, graphite, carbon fiber, or carbon nanotube may be
used as the electrical conducting material.

[0042]The electrode patterns 12a and 12b may be formed on the collector 11
using the inkjet method or the like. As shown in FIG. 1, all of the
electrode patterns 12a are formed in rectangular shapes and have
generally the same size (area) (including manufacturing error). Also, the
thickness of the electrode patterns 12a (i.e., the length in the Z
direction) is substantially the same value (including manufacturing
error) in all of the electrode patterns 12a. Furthermore, the plurality
of electrode patterns 12a are arranged in a matrix in the X-Y plane.
Also, an ion conducting layer 13 having the same shape as the electrode
patterns 12a and 12b is formed on the electrode patterns 12a and 12b of
the bipolar electrode 1. This ion conducting layer 13 may be formed of a
solid polyelectrolyte having ion conductivity (such as polyethylene oxide
or polypropylene oxide).

[0043]Incidentally, in an electrode used in a non-bipolar type battery, a
polymer gel electrolyte may be used as the ion conducting layer 13. In
the first example embodiment, the ion conducting layer 13 is formed in
the same shape as the electrode patterns 12a and 12b, but it is not
limited to this. For example, a plate-shaped electrolyte membrane or a
plate shaped body in which a separator has been impregnated with an
electrolyte may also be used. As shown in FIG. 1, the intervals between
two adjacent electrode patterns 12a in the Y direction among the
plurality of electrode patterns 12a, are different. That is, the
intervals between adjacent electrode patterns 12a are set to gradually
become smaller from the central portion of the bipolar electrode (i.e.,
the collector 11) toward the outer peripheral portion.

[0044]More specifically, as shown in FIG. 1, it is assumed that an
interval between an electrode pattern 12a positioned at the central
portion of the collector 11 and an electrode pattern 12a adjacent to this
electrode pattern 12a in the Y direction, i.e., the length in the Y
direction of a region where no electrode pattern 12a is formed at the
central portion of the collector 11, is "dl". Similarly, it is assumed
that an interval between an electrode pattern 12a positioned on an outer
peripheral portion (i.e., an end portion) of the collector 11 and an
electrode pattern 12a that is adjacent to this electrode pattern 12a in
the Y direction is "dn". Also, it is assumed that an interval between
adjacent electrode patterns 12a in an arbitrary position in the Y
direction is "dk". In this case, the relationship between dl, dn, and dk
is such that dl> . . . dk>dk-1> . . . dn. Here, "k" is an
arbitrary value within a range of 1 to n. Also, the interval (dl . . .
dn) between adjacent electrode patterns 12a may be set taking into
account the temperature distribution curve of a typical bipolar electrode
(i.e., an electrode in which an electrode layer is formed on the entire
surface of a collector).

[0045]In the graph in FIG. 3, the temperature distribution curve of a
typical bipolar electrode is shown by the dotted line. The vertical axis
of the graph represents the temperature on the bipolar electrode and the
horizontal axis represents the position (i.e., the position in the Y
direction in FIG. 1) on the bipolar electrode. As shown by the dotted
line in FIG. 3, with a typical bipolar electrode, heat tends to build up
in the central portion so the temperature at the central portion is
higher than it is at any other portion. The temperature gradually drops
from the central portion of the bipolar electrode toward the outer
peripheral portion. This is because heat escapes easier on the outer
peripheral portion side of the bipolar electrode. Incidentally, even when
a plurality of electrode patterns (minute cells) are arranged in a matrix
at equal intervals as described in JP-A-2005-11660, a temperature
distribution curve is similar to that shown by the dotted line in FIG. 3.
Taking the temperature distribution curve shown by the dotted line in
FIG. 3 into account, it is preferable to make the interval (dl) between
the electrode patterns 12a at the central portion the widest and make the
intervals between the electrode patterns 12a gradually smaller toward the
outer peripheral portion sides. Arranging the electrode patterns 12a in
this way enables the temperature distribution curve on the bipolar
electrode 1 that is shown by the solid line in FIG. 3 to be obtained.
That is, the heat radiation efficiency on the central portion side of the
bipolar electrode 1 may be improved, and variation in the temperature
distribution of the bipolar electrode 1 may be suppressed. In particular,
making the intervals between the electrode patterns 12a gradually larger
from the outer peripheral portion side toward the central portion side
enables the temperature distribution of the bipolar electrode 1 to be
made substantially uniform.

[0046]With the bipolar battery of the first example embodiment, spaces S
are formed between stacked collectors 11, as shown in FIG. 2. Here, the
intervals between adjacent electrode patterns 12a on the central portion
side of the bipolar electrode 1 are wider than the intervals between
adjacent electrode patterns 12a on the outer peripheral portion side so
the spaces S on the central portion side are larger than the spaces S on
the outer peripheral portion side. Therefore, heat generated on the
central portion side of the bipolar electrode 1 may escape easier to the
outside via the relative large spaces S, thereby improving the heat
radiation efficiency on the central portion side of the bipolar
electrode. Incidentally, cooling air may be supplied into the spaces S
from outside of the bipolar battery. In this case, an increase in the
temperature on the bipolar electrode may be efficiently suppressed.

[0047]Incidentally, in this first example embodiment, the intervals
between adjacent electrode patterns 12a in the Y direction are made
gradually larger from the outer peripheral portion of the collector 11
toward the central portion, but the invention is not limited to this.
More specifically, the invention may also include a case in which the
intervals between adjacent electrode patterns 12a are the same in one
region (for example, a case in which dk=dk-1; see FIG. 1). That is, even
if the intervals between adjacent electrode patterns 12a are not made
different, as long as the temperature difference on the bipolar electrode
1 is substantially zero, the intervals between adjacent electrode
patterns 12a may be set at the same value. According to this first
example embodiment, by forming the plurality of electrode patterns 12a
(12b) on the collector 11, heat distortion in a specific direction (the X
direction or the Y direction) of the bipolar electrode 1 may be
suppressed even if the temperature of the battery changes or the
respective thermal expansion coefficients of the collector 11, the
electrode patterns 12a and 12b, and the ion conducting layer 13 are
different. Moreover, cracking or the like of the electrode layer due to
stress applied to the bipolar electrode may be suppressed compared with a
case in which an electrode layer is formed on the entire surface of the
collector 11. Also, forming the plurality of electrode patterns 12a (12b)
at intervals enables the bipolar electrode 1 to bend easily so the
bipolar electrode 1 may be arranged along a curved surface. This improves
the degree of freedom with respect to the location where the battery may
be arranged.

[0048]Here, a cylindrical battery may also be formed by rolling up the
bipolar electrode (or an electrode other than a bipolar electrode). More
specifically, as shown in FIG. 4, a plurality of electrode patterns 12a'
that extend in the Y direction are formed on the collector 11. Here, the
widths (i.e., the length in the X direction) of the plurality of
electrode patterns 12a' are substantially the same. Also, the intervals
between adjacent electrode pattern 12a' in the X direction gradually
become smaller from the lower side to the upper side in FIG. 4. However,
a portion may also be included in which the intervals between adjacent
electrode patterns 12a' in the X direction are substantially the same
(including manufacturing error).

[0049]Then, the cylindrical battery is formed by rolling up a bipolar
electrode 1' shown in FIG. 4 along the direction shown by the arrowed
line from the end portion positioned on the lower side in FIG. 4. In the
cylindrical battery formed by rolling up a single bipolar electrode in
this way, heat tends to remain in the inner region in the radial
direction (i.e., the stacking direction of the bipolar electrode) more
than it does in the outer region in the radial direction. Therefore, the
heat radiation on the radially inner region may be improved by making the
intervals between adjacent electrode patterns 12a' in the radially inner
region (i.e., the region on the lower side in FIG. 4) wider than the
intervals between adjacent electrode patterns 12a' in the radially outer
region (i.e., the region on the upper side in FIG. 4), as shown in FIG.
4. Therefore, variation in the temperature distribution may be suppressed
in a cylindrical battery as well.

[0050]On the other hand, the bipolar battery of the first example
embodiment is structured such that a bipolar battery 100 is sandwiched on
both sides (i.e., in the stacking direction of the bipolar electrode 1)
by retaining members 200, as shown in FIG. 5, in order to suppress
thermal expansion at the bipolar electrode 1. More specifically, the
retaining members 200 sandwich the bipolar battery 100 on the outer
peripheral portion sides of the bipolar battery 100, as shown by the
arrows in FIG. 5. This structure enables thermal expansion to be
suppressed on the outer peripheral portion sides of the bipolar batter
100 but not on the central portion side. As a result, only the region on
the central portion side may be displaced by thermal expansion. Using the
bipolar electrode 1 of the first example embodiment, however, enables
this thermal expansion on the central portion side of the bipolar
electrode 1 to be suppressed because the heat radiation efficiency on the
central portion side of the bipolar electrode 1 is higher than the heat
radiation efficiency on the outer peripheral portion side. Thus, it is
possible to suppress only the region on the central portion side of the
bipolar battery 100 from being displaced due to thermal expansion even
when the structure shown in FIG. 5 is used.

[0051]Incidentally, in the first example embodiment, the intervals between
adjacent electrode patterns 12a are made different in the Y direction, as
shown in FIG. 1, but the invention is not limited to this. That is, the
intervals between adjacent electrode patterns 12a may be made different
in the X direction, or the intervals between adjacent electrode patterns
12a may be made different in both the X direction and the Y direction. In
this case as well, the intervals between the electrode patterns 12a on
the central portion side of the bipolar electrode 1 only need to be made
larger than the intervals between the electrode patterns 12a on the outer
peripheral portion side. Here, variation in the temperature distribution
in the X and Y directions of the bipolar electrode 1 may be suppressed by
making the intervals between adjacent electrode patterns 12a different in
the X and Y directions.

[0052]Also, in the first example embodiment, each of the electrode
patterns 12a is formed in a rectangular shape, but the invention is not
limited to this. That is, the electrode patterns may also be formed in a
variety of other shapes as well. For example, the electrode patterns may
be circular or polygonal such as triangular. Also, electrode patterns of
different shapes may also be formed on the collector.

[0053]Furthermore, in the first example embodiment, the plurality of
electrode patterns 12a are arranged in a matrix as shown in FIG. 1, but
the invention is not limited to this. For example, electrode patterns may
be concentrically arranged around an electrode pattern that is arranged
at the central portion of the bipolar electrode. In this case as well,
the intervals between adjacent electrode patterns on the central portion
side of the bipolar electrode are set wider than the intervals between
adjacent electrode patterns on the outer peripheral portion side.
Arranging electrode patterns concentrically in this way enables variation
in the temperature distribution in every direction in the X-Y plane to be
suppressed in the bipolar electrode.

[0054]Also, in this example embodiment, the plurality of electrode
patterns 12a are arranged in a matrix in the X-Y plane as shown in FIG.
1, but a plurality of electrode patterns 22a that extend in the X
direction may also be arranged lined up in the Y direction as shown in
FIG. 6. In this case as well, the intervals between adjacent electrode
patterns 22a are set so that they become smaller from the central portion
of the collector 11 toward the outer peripheral portion.

[0055]Moreover, in the first example embodiment, the thickness (i.e., the
length in the Z direction in FIG. 2) of each electrode pattern 12a formed
on the collector 11 is set at substantially the same value for all of the
electrode patterns 12a, but the invention is not limited to this. That
is, the thickness of the electrode patterns 12a may be changed depending
on the position of the electrode pattern 12a on the collector 11. More
specifically, of two adjacent electrode patterns in a specific direction
(such as the X direction or the Y direction), an electrode pattern
positioned on the central portion side may be made thinner than an
electrode pattern positioned on the outer peripheral portion side. Also,
as shown in FIG. 7, electrode patterns 32a may be made gradually thinner
from the outer peripheral portion of the bipolar electrode toward the
central portion (t1<t2<t3). However, at least two electrode
patterns having substantially the same thickness (including manufacturing
error) may also be included. In this way, when the thicknesses of the
electrode patterns 32a are different, the thickness of the ion conducting
layer (which corresponds to the ion conducting layer 13 shown in FIG. 2)
is also different. That is, the intervals between two stacked collectors
is fixed so if the thicknesses of the electrode patterns 32a are
different, then the thickness of the ion conducting layer is different.
As described above, if the electrode patterns 32a on the central portion
side of the collector 11 are made thinner, the current density at the
central portion side is reduced, thereby enabling heat generation on the
central portion side to be suppressed. This makes it possible to suppress
variation in the temperature distribution on the bipolar electrode.

[0056]On the other hand, the density of the active material of which the
electrode patterns 12a are made (i.e., the volume of the active material
of the positive electrode that accounts for the electrode patterns 12a)
may be made different depending on the position on the collector 11. More
specifically, the density of the active material of an electrode pattern
12a positioned on the central portion side of the bipolar electrode 1 may
be made lower than the density of the active material of an electrode
pattern 12a positioned on the outer peripheral side. Also, the density of
the active material of the electrode patterns 12a may be gradually
reduced from the outer peripheral portion toward the central portion.
However, at least two electrode patterns having substantially the same
density of the active material (including manufacturing error) may also
be included. By reducing the density of the active material of the
electrode patterns 12a positioned on the central portion side as
described above, the current density on the central portion side may be
reduced, thereby suppressing heat generation on the central portion side.
This makes it possible to suppress variation in the temperature
distribution on the bipolar electrode.

[0057]Also, taking the temperature distribution on the bipolar electrode
into account, the electrode patterns may also be formed based on three
parameters, i.e., the intervals between the electrode patterns, the
thickness of the electrode patterns, and the density of the active
material of the electrode patterns. By making not only the intervals
between the electrode patterns 12a different but also the thickness of
the electrode patterns and the density of the active material different,
the region where no electrode patterns are formed on the surface of the
collector 11 may be made smaller.

[0058]On the other hand, in the first example embodiment, the electrode
patterns are arranged differently on the bipolar electrode. However, in a
bipolar battery in which bipolar electrodes are stacked, the electrode
patterns may be arranged differently depending on their position in the
direction of thickness (i.e., the stacking direction of the bipolar
electrodes) of the battery. Here, with a bipolar battery having a stacked
structure, the ease with which heat escapes on the center layer side in
the stacking direction is different from that on the outer layer side in
the stacking direction so the temperature distribution on each bipolar
electrode is different. Therefore, by making the arrangement of the
electrode patterns on the bipolar electrode different depending on the
position of the bipolar electrode in the stacking direction, variation in
the temperature distribution may be suppressed in each bipolar electrode
in the stacking direction.

[0059]More specifically, when comparing an interval between electrode
patterns of a bipolar electrode positioned on the center layer side in
the stacking direction and an interval which is in a corresponding
position between electrode patterns of a bipolar electrode positioned on
the outer layer side in the stacking direction, the interval between
electrode patterns of the bipolar electrode positioned on the center
layer side may be set larger than the interval in a corresponding
position between electrode patterns of the bipolar electrode positioned
on the outer layer side. For example, an interval dl (see FIG. 1) between
electrode patterns of the bipolar electrode positioned on the center
layer side may be set wider than a corresponding interval dl between
electrode patterns of the bipolar electrode positioned on the outer layer
side.

[0060]On the other hand, the bipolar electrode may also be structured as
shown in FIG. 8. Here, FIG. 8 is a front view of the concentric bipolar
electrode. In the structure shown in FIG. 8, a plurality of electrode
patterns 12a'' are formed substantially concentrically on a substantially
circular collector 11. Here, the widths (i.e., lengths in the radial
direction) of the electrode patterns 12a'' are substantially the same
(including manufacturing error). Also, the intervals between adjacent
electrode patterns 12a'' in the radial direction gradually increase from
the outer peripheral portion toward the central portion. However, a
portion in which the intervals between adjacent electrode patterns 12a''
are substantially the same (including manufacturing error) may also be
included. In the structure of a bipolar electrode 1'' shown in FIG. 8,
heat tends to remain in the inner region in the radial direction more
than it does in the outer region in the radial direction. Therefore, by
making the intervals between the electrode patterns 12a'' on the inside
in the radial direction wider than the intervals between the electrode
patterns 12a'' on the outside in the radial direction, as described
above, the heat radiation on the inside in the radial direction may be
improved. This makes it possible to suppress variation in the temperature
distribution in the X-Y plane.

[0061]Here, a cylindrical battery may be formed by stacking a plurality of
the bipolar electrodes 1'' shown in FIG. 8 in the Z direction.
Incidentally, when stacking the plurality of bipolar electrodes 1'', the
temperature of the bipolar electrode 1'' positioned on the center layer
side may become higher than the temperature of the bipolar electrode 1''
positioned on the outer layer side. Therefore, the structure of the
bipolar electrode 1'' on the center layer side (more specifically, the
intervals between adjacent electrode patterns 12a '') may be made
different from the structure of the bipolar electrode 1'' on the outer
layer side. For example, the intervals between the adjacent electrode
patterns 12a'' in a corresponding region in the stacking direction (i.e.,
the Z direction) may be made different. More specifically, the intervals
between adjacent electrode patterns 12a'' of the bipolar electrode 1'' on
the center layer side may be made wider than the corresponding intervals
between the adjacent electrode patterns 12a'' of the bipolar electrode
1'' on the outer layer side. This also makes it possible to suppress
variation in the temperature distribution in the stacking direction.
Incidentally, in addition to the structures shown in FIGS. 4 and 8, the
thickness of the electrode patterns may be made different as shown in
FIG. 7, and the density of the active material included in the electrode
patterns may also be made different.

[0062]Next, a bipolar battery according to a second example embodiment of
the invention will be described with reference to FIG. 9.

[0063]FIG. 9 is a front view of a portion of a bipolar electrode used in
the bipolar battery of this example embodiment. In the first example
embodiment described above, the intervals between adjacent electrode
patterns in the Y direction are different. In the second example
embodiment, however, the intervals between adjacent electrode patterns
42a are substantially the same (including manufacturing error), but the
sizes (areas) of the electrode patterns 42a are different, respectively.
More specifically, as shown in FIG. 9, the size (i.e., the width in the Y
direction) of the electrode patterns 42a is reduced from the outer
peripheral portion side of the bipolar electrode (collector) toward the
central portion side. That is, the intervals between adjacent electrode
patterns 42a in the Y direction are all a fixed value "dk" (which is an
arbitrary value), while the widths W1 to W5 of the electrode patterns 42a
are such that "W5>W4>W3>W2>W1". Even with the structure shown
in FIG. 9, the formation density of the electrode patterns 42a on the
central portion side of the bipolar electrode may be made less than the
formation density of the electrode patterns 42a on the outer peripheral
portion side, thereby enabling the heat radiation efficiency on the
central portion side of the bipolar electrode to be improved. This makes
it possible to suppress variation in the temperature distribution on the
bipolar electrode.

[0064]Incidentally, in the structure shown in FIG. 9, the widths W1 to W5
of all of the electrode patterns 42a lined up in the Y direction are
different. However, at least two electrode patterns that have
substantially the same widths may also be included. Also, even in the
structure in this second example embodiment, the thickness of the
electrode patterns 42a may be made different or the density of the active
material of which the electrode patterns are formed may be made
different, as described in the first example embodiment. Further, in the
bipolar battery having a stacked structure, the structures of the
electrode patterns on the bipolar electrode may be made different
depending on the position of the bipolar electrode in the stacking
direction. More specifically, when comparing an electrode pattern 42a of
a bipolar electrode positioned on the center layer side with an electrode
pattern 42a, which is in a corresponding position, of a bipolar electrode
positioned on the outer layer side, the width of the electrode pattern
42a of the bipolar electrode positioned on the center layer side may be
made smaller than the width of the electrode pattern 42a, which is in a
corresponding position, of the bipolar electrode positioned on the outer
layer side. As a result, the heat radiation efficiency may be made
different depending on the position in the stacking direction, which
makes it possible to suppress variation in the temperature distribution
also in the stacking direction of the bipolar battery.

[0065]Also, the structures shown in FIGS. 4 and 8 described in the first
example embodiment may also be applied to the second example embodiment.
That is, in the structures of the bipolar electrodes shown in FIGS. 4 and
8, the widths of the electrode patterns are substantially constant while
the intervals between adjacent electrode patterns are different. However,
the intervals between adjacent electrode patterns may be made
substantially constant while the widths of the electrode patterns may be
made different. More specifically, in the structure of the bipolar
electrode shown in FIG. 4, the intervals between adjacent electrode
patterns in the X direction may be made substantially the same while the
widths (i.e., the lengths in the X direction) of the electrode patterns
positioned on the upper side in FIG. 4 may be made narrower than the
widths of the electrode patterns positioned on the lower side in FIG. 4.
Also, in the structure of the bipolar electrode shown in FIG. 8, the
intervals between adjacent electrode patterns in the radial direction may
be made substantially the same while the widths of the electrode patterns
positioned on the central portion may be made narrower than the widths of
the electrode patterns positioned on the outer peripheral side.
Incidentally, in addition to the structure described above, as described
with FIG. 7 and the like, the thicknesses of the electrode patterns may
be made different or the densities of the active material included in the
electrode patterns may be made different. The same effects obtained with
the structures shown in FIGS. 4 and 8 may be obtained with the foregoing
structure as well. That is, it is possible to suppress variation in the
temperature distribution on the bipolar electrode.

[0066]Meanwhile, in the foregoing first and second example embodiments,
the electrode patterns that serve as the positive electrode layer and the
electrode patterns that serve as the negative electrode layer have the
same structure. However, it is also possible to have only one of those
electrode layers be structured as described in the foregoing first or
second example embodiments. In this case, the structure of the other
electrode layer may be such that an electrode layer is formed on the
entire surface of the collector. Also, the secondary battery or capacitor
described in the foregoing first and second example embodiments may be
used as a power storing apparatus for driving a motor in, for example, an
electric vehicle (EV), a hybrid vehicle (HEV), or a fuel cell vehicle
(FCV).

[0067]On the other hand, in the foregoing first and second example
embodiments, the structure of the electrode patterns is set taking into
account heat radiation characteristics of the bipolar battery itself.
However, the electrode patterns may also be formed taking into account
the heat radiation characteristics of the bipolar battery that are
associated with thermal effects from the outside. This will now be
described in detail. For example, when a heat source (such as an engine
or a motor) is arranged near the bipolar battery, a region on the heat
source side of the bipolar battery may be less able to radiate heat than
other regions due to the fact that the region is thermally effected by
the heat source. Therefore, by making the formation density of the
electrode patterns in the region on the heat source side lower than the
formation density of the electrode patterns in other regions, variation
in the temperature distribution of the electrode pattern may be
suppressed. That is, as in the foregoing first and second example
embodiments, by making the formation density of the electrode patterns
different, the heat radiation on the bipolar electrode may be improved,
thereby suppressing a temperature increase on the bipolar electrode.

[0068]Here, the formation density of the electrode patterns may be set by
taking into account the temperature distribution characteristics on the
bipolar electrode based on the thermal effects from the heat source. For
example, in addition to the structures of the bipolar electrodes
described in the foregoing first and second example embodiments, the
formation density of the electrode patterns in the region on the heat
source side (i.e., the region on one of the outer peripheral portion
sides) may be made lower than the formation density of the electrode
patterns in another region (i.e., the region on the other outer
peripheral portion side). Also, when the temperature increase is the
greatest (when the heat radiation is the lowest) in the region on the
heat source side of the bipolar electrodes due to the thermal effect from
the heat source, the formation density of the electrode patterns in the
region on the heat source side may be made the lowest.

[0069]On the other hand, with respect to a bipolar battery in which
bipolar electrodes are stacked, when the heat source is arranged in the
stacking direction, the formation densities of the electrode patterns in
the corresponding region in the stacking direction of the plurality of
bipolar electrodes may be made different. More specifically, of the
plurality of stacked bipolar electrodes, the formation density of the
electrode patterns of the bipolar electrode(s) (one or a plurality
thereof) positioned on the heat source side (i.e., on one of the
outermost layer sides in the stacking direction) may be made lower than
the formation density of the electrode patterns of another bipolar
electrode (such as a bipolar electrode positioned on the other outermost
layer side in the stacking direction). In this case, the formation
density of the electrode patterns of the bipolar electrode positioned on
the center layer side in the stacking direction and the outermost layer
side on the heat source side may be made lower than the formation density
of the electrode patterns on the other bipolar electrode. This structure
makes it possible to suppress variation in the temperature distribution
in the stacking direction. Incidentally, when the heat radiation
characteristics of the bipolar electrode positioned on the outermost
layer side on the heat source side are the lowest, the formation density
of the electrode patterns on this bipolar electrode may also be made the
lowest. Methods for making the formation densities of the electrode
patterns different include changing the intervals between adjacent
electrode patterns (see FIG. 1), changing the thickness of the electrode
patterns (see FIG. 7), and changing the size of the electrode patterns,
as described in the foregoing first and second example embodiments.

[0070]While the invention has been described with reference to example
embodiments thereof, it is to be understood that the invention is not
limited to the described embodiments or constructions. To the contrary,
the invention is intended to cover various modifications and equivalent
arrangements. In addition, while the various elements of the example
embodiments are shown in various combinations and configurations, other
combinations and configurations, including more, less or only a single
element, are also within the scope of the invention defined in the
claims.